docs(ia): reconcile capabilities/ into the 9 pillar folders (one IA, redirected)

[rickylabs]

Part of #401

Handle: S0 · Milestone: 0.0.1-beta.7 · Lane: WSL Codex daemon-attached (structural, not prose). HARD PRECURSOR — blocks all C/D authoring.

Scope

Promote every docs/site/capabilities/*.md page into its target pillar folder per the mapping in proposal §2.2; add a URL redirect for each old /capabilities/<x>/ path; retarget every comp.xref({ key: "cap:<x>" }) to the new pillar path; update _data.ts "Overview & Concepts" cards on the 3 pillars that route into capabilities/; add the two net-new pillar leaf stubs (orchestration-runtime/cli-scaffold.md, ai/mcp.md) as empty-but-navigable placeholders for D to fill; delete capabilities/index.md after redirects land.

Explicit non-goals: do NOT touch tutorial-chapter nav anchors (Topic-C's surface); do NOT rewrite page prose (that is D's job — move content as-is); no framework source.

Acceptance

• deno task verify green in docs/site (build → check:links → check:caveats) — zero broken internal links.
• Every old /capabilities/<x>/ URL 301/redirects to its new pillar path (manual curl/nav check of all 15 moved pages).
• capabilities/ no longer referenced by any comp.xref key or _data.ts entry (grep clean).
• _data.ts nav renders the 9 pillars unchanged in count/order; the 3 rerouted "Overview & Concepts" cards point at in-pillar leaves.
• Two new leaf stubs exist and are reachable from nav.
• No packages//plugins/ file touched; no deno.lock churn.

Design source: design/CD-docs/epic-and-issues.md (§2, S0).